1. Field of the Invention
The present invention relates to an image forming device, such as a laser printer or a photocopier, heating a fixing unit by alternating current (AC) power. More particularly, the present invention relates to an image fixing control system and method to increase the quality of a fixed image by preventing the occurrence of overshoot or undershoot according to a temperature variation of a heating roller.
2. Description of the Related Art
A heating circuit of a general fixing unit used for laser printers and photocopiers includes a part transferring from a main controller, a control signal for determining whether power is supplied to the fixing unit, a triac for applying alternating current (AC) power to the fixing unit, and a triac driver (for example, a photo coupler) driving a triac.
A conventional fixing circuit for a laser printer performs a simple temperature control by receiving AC power from a power supply and applying the AC power to the fixing circuit. When a main controller detects a temperature of a fixing unit using a temperature sensor and if the main controller determines, according to the detected temperature, that a temperature increase is needed, the main controller applies the AC power to the fixing unit. If the main controller determines, according to the detected temperature, that a temperature decrease is needed, the main controller cuts off the AC power to the fixing unit.
When the AC power is initially applied to the fixing circuit, the main controller quickly heats a heating roller by transmitting a turn-on signal to the fixing unit at a full duty ratio. When the heating roller reaches a predetermined maximum temperature, the main controller decreases a temperature of the heating roller by transmitting a turn-off signal to the fixing unit.
According to a conventional fixing unit control system, since a temperature of a heating roller varies very quickly when the heating roller is initially heated, a function of fixing an image on a print medium is degraded. Accordingly, there is a need for an improved system for and method for efficiently controlling image fixing.